Electrical submersible pump assemblies (ESP) are commonly employed to pump well fluid from oil producing wells. A typical ESP has a pump driven by an electrical motor filled with a dielectric motor lubricant. A pressure equalizer or seal section cooperatively connects with the motor to reduce a pressure differential between the motor lubricant and well fluid on the exterior.
One type of seal section employs bellows, typically metal. The seal section has an inner axially extending guide tube located within a cylindrical housing. In one arrangement, an outer bellows has one end fixed to an end of the housing and another end free to float or move axially. An inner bellows of smaller outer diameter has a fixed end secured to an opposite end of the housing and a floating end fixed to the floating end of the outer bellows. When the hydrostatic pressure differs from the motor lubricant pressure, one of the bellows extends while the other contracts to equalize the motor lubricant pressure with the hydrostatic pressure. Extension and contraction may occur while running the ESP into the well. Extension and contraction also occurs as the motor lubricant heats and cools. Heating and cooling occurs each time the motor re-starts after being turned off.
The inner diameter of the corrugated flexible wall of the inner bellows will contact and slide along the guide tube during extension and contraction of the inner bellows. Similarly, the outer diameter of the corrugated flexible wall of the outer bellows will contact and slide along the inner surface of the housing during extension and contraction of the outer bellows. The sliding movement of the inner diameter portions of the inner bellows against the guide tube can cause wear of the thin corrugated wall. The sliding movement of the outer diameter portions of the outer bellows against the inner surface of the housing can cause wear of the thin corrugated wall of the outer bellows. As larger volume, longer inner and outer bellows are developed, the extent of the sliding, rubbing contact increases because the axial travel range of the floating ends increases. The wear of the thin metal of the inner and outer bellows can result in a reduced fatigue life.